The detection of tumorous lesions in the breast has progressed from early observation and palpation procedures to a variety of somewhat sophisticated imaging systems. A consequence of these advances in tumor detection is the identification of suspect tumor at an early stage in its development. Generally, at such early stages the suspect tumor may be somewhat small. Rather than resort immediately to an open surgical resection upon such early detection, practitioners generally carry out a preliminary, minimally invasive biopsy procedure. Such preliminary biopsy approaches are of importance, inasmuch as statistically, only 20% of these small tumors will be found to be malignant. Tumors determined to be benign have been left in situ with no excision. Over one million of these biopsies are performed in the United States each year, the procedure providing for the removal of part or all the suspect tissue for pathology examination and diagnosis. See generally:                (1) Rosen, Paul Peter, “Rosen's Breast Pathology”, Lippincott-Raven Publishers, Philadelphia, 1997 pp 837-858.        
One of the minimally invasive options is needle biopsy which may be either fine needle aspiration (FNA) or large core. Fine needle aspiration (FNA) is a procedure in which a fine needle, for example, of 21 to 23 gauge, having one of a number of tip configurations, such as the Chiba, Franzeen or Turner, is inserted into the breast and guided to the tumor site. A vacuum is created and the needle moved up and down along the tumor to assure that it collects targeted cellular material. Generally, three or more passes will be made to assure the collection of sufficient sample. Then, the needle and tissue sample are withdrawn from the breast for analysis.
The resulting specimen is subject to cytologic assay. In this regard, cell structure and related aspects are studied. This analysis has been used to improve or customize the selection of chemotherapeutic agents with respect to a particular patient.
While a fine needle aspiration biopsy has the advantage of being relatively simple, there are some drawbacks associated with its use. With fine needle aspiration, there remains a risk of false-negative results, which most often occur in cases involving extremely fibrotic tumor. In addition, after the procedure has been performed there may be insufficient specimen material for diagnosis. Finally, with fine needle aspiration alone the entire area of suspect tissue is not removed. Rather fragmented portions of tissue are withdrawn which do not allow a more advanced pathological investigation.
This limitation also is observed with respect to large core needle biopsies. For a large core needle biopsy, a 14 to 18 gauge needle is inserted in the breast having an inner trocar with a sample notch at the distal end and an outer cutting cannula. Similar to a fine needle aspiration, tissue is drawn through a needle by vacuum suction. These needles have been combined with biopsy guns to provide automated insertion that makes the procedure shorter and partially eliminates location mistakes caused by human error or lesion displacement. Once inserted, multiple contiguous tissue samples may be taken at a time.
Samples taken during large core needle biopsies may be anywhere from friable and fragmented to large pieces 20 to 30 mm long. These samples may provide some histological data, unlike fine needle aspiration samples. However, they still do not provide optimum pathological information. For further information concerning needle biopsy procedures see the following:                (2) Parker, Steve H, “Needle Selection and Steriotatic Large-Core Breast Biopsy”, Percutaneous Breast Biopsy Eds. Parker, et al, Raven Press, New York, 1993 pp 7-14 and 61-79.        
A device, which is somewhere between a needle biopsy and open surgery, is referred to as the Advanced Breast Biopsy Instrumentation (ABBI). With the ABBI procedure, the practitioner, guided by appropriate imaging, removes a core tissue sample of 5 mm to 20 mm in diameter. While the ABBI has the advantage of providing a large tissue sample similar to that obtained from an open surgical biopsy, the cylindrical tissue sample is taken from the subcutaneous tissue to an area beyond the suspect tumor. For tumors embedded more deeply within the breast, the amount of tissue removed is considerable. In addition, while less expensive than open surgical biopsy, the ABBI has proven expensive compared to other biopsy techniques, and it has been noted that the patient selection for ABBI is limited by the size and location of the tumor, as well as by the presence of very dense parenchyma around the tumor. See the following publications:                (3) Parker, Steve H., “The Advanced Breast Biopsy Instrumentation: Another Trojan Horse?”, Am. J. Radiology 1998; 171:51-53.        (4) D'Angelo, Philip C., et al., “Sterotatic Excisional Breast Biopsies Utilizing The Advanced Breast Biopsy Instrumentation System”, Am. J. Surg. 1997; 174: 297-302.        (5) Ferzli, George S., et al., “Advanced Breast Biopsy Instrumentation: A Critique”, J. Am. Coll. Surg., 1997; 185:145-151.        
Another biopsy approach has been referred to as the mammotome and the Minimally Invasive Breast Biopsy (MIBB). These devices carry out a vacuum-assisted core biopsy wherein fragments of suspect tissue are removed with an 11-14 gauge needle. While being less invasive, the mammatome and MIBB yield only a fragmentary specimen for pathological study. These devices therefore are consistent with other breast biopsy devices in that the degree of invasiveness of the procedure necessarily is counterbalanced against the need of obtaining a tissue sample whose size and margins are commensurate with pathology requirements for diagnosis and treatment.
A minimally invasive approach to accessing breast lesions wherein the lesion is partially removed or removed in its entirety for diagnostic as well as therapeutic purposes has been described in U.S. Pat. No. 6,277,083 by Eggers, et al., entitled “Minimally Invasive Intact Recovery Of Tissue”, issued Aug. 21, 2001. The instrument described includes a tubular delivery cannula of minimum outer diameter, the tip of which is positioned in confronting adjacency with a tissue volume to be removed. Following such positioning, the electrosurgically excited leading edge of a capture component is extended forwardly from the instrument tip to enlarge while electrosurgically cutting and surrounding or encapsulating a tissue volume, severing it from adjacent tissue. Following such capture, the instrument and the encaptured tissue volume are removed through an incision of somewhat limited extent.
An improved design for this instrument, now marketed under the trade designation EN-BLOC® by Neothemia Corporation of Natick Mass., is described in U.S. Pat. No. 6,471,659 by Eggers, et al., entitled “Minimally Invasive Intact Recovery Of Tissue”, issued Oct. 29, 2002. The EN-BLOC® instrumentation includes a tubular delivery cannula of minimum outer diameter, the tip of which is positioned in confronting adjacency with the target tissue volume to be removed. Such positioning is facilitated through the utilization of a forwardly disposed precursor electrosurgical electrode assembly. Located within the interior channel of this delivery cannula is a capture component configured with five relatively elongate thin leafs mutually interconnected at their base to define a pentagonal cross-sectional configuration. Each of the leafs terminates forwardly at a tip with a transversely bent eyelet structure. Slidably extending through each eyelet is an electrically conductive pursing cable of a pursing cable assembly, which extends to an attachment with another adjacent leaf tip. This cable extends rearwardly through a small guide tube attached to a leaf for connection with the slidable cable terminator component of a drive assembly. The drive assembly is driven forwardly by an electric motor through a translation assembly. By adjusting the location of a stop component, which engages the cable terminator component, the size of a captured specimen may be varied. For example, the device can be configured to recover tissue specimens of 10 mm, 15 mm, 20 mm or 25 mm effective maximum diametric extent. As the cable terminator component is pulled by the cable assembly into abutting engagement with the stop component, the cables are tensioned to draw the leaf eyelet structures together in a pursing action.
Cabling involved with this instrument must quite diminutive in size while retaining adequate tensile strength in the temperature environment of an electrosurgical cutting arc. That temperature has been computationally estimated as being between about 1400° F. and 1600° F. Heretofore, cable having a nominal diameter of 0.006 inch has been employed. Structured with nineteen type 304 stainless steel strands having a diameter of about 0.0012 inch, the cable exhibited that flexibility requisite for feeding through the capture component leaf eyelets while creating a leading edge cutting arc. While this electrosurgical cutting arc is present, the cables further must sustain not only stresses associated with the forward movement of the capture component, but also those loads imposed by the encapturing pursing activity during which the eyelets are drawn together to complete encapsulation of the tissue sample. That configuration at pursing completion has been referred to as a “basket”. Maximum loads are sustained by the cables at the completion of pursing movement. At that point in time, there is no movement and no frictional loss component and the cables are called upon to sustain loads imposed by the motor drive of the instrument as it enters a stall status. The latter stall condition, developing a 130 milliamp current spike, is detected to terminate the capture sequence. Test based experience with the instrument has determined that the load carrying capability of this cable structure at the noted elevated temperatures may be exceeded. While greater tensile strength is called for, no substantial increase in strand and thus cable diameter can be made due to the necessity of achieving a sufficient flexure or play-out as the cables pass through the leaf tip eyelets. Thus, improved strength at high temperatures is required without a compromise of cable deployment characteristics. Unacceptable increases in cable diametric size also would increase the power required for electrosurgical cutting.
The tip located eyelet structures, have heretofore been formed integrally with the thin (0.003 inch) capture component leafs. Because it is necessary to twist the eyelet structures to achieve necessary cable play-out or deployment, the eyelet structures have been configured with a narrow neck portion of 0.020 inch width and an overall length of about 0.080 inch. With the arrangement, the eyelets were twisted at the neck portion. Test experience with the capture components utilizing compressed porcine tissue has determined that, where the retrieval procedures encounter very dense breast tissue, the eyelets may fail by folding back. This is particularly the case where the instruments are structured for larger capture diameters, i.e., in the range of from about 15 mm to about 25 mm.